This thread is resolved. Here is a description of the problem and solution.
Problem: If you're experiencing a TypeError with the message 'Illegal offset type in isset or empty' on your site, it might be due to a conflict between WPML and the latest version of the Site Kit by Google plugin. Solution: We recommend downgrading to the previous version of the Site Kit by Google plugin (1.105) after ensuring you have a full site backup. This issue is currently under investigation by our developers. For more details, please check the known issue here: https://wpml.org/errata/site-kit-by-google-uncaught-typeerror-illegal-offset-type-in-isset-or-empty-in/.
If this solution does not apply to your case, or if it seems outdated, we highly recommend checking related known issues at https://wpml.org/known-issues/, verifying the version of the permanent fix, and confirming that you have installed the latest versions of themes and plugins. If you need further assistance, please open a new support ticket.
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This may be related to the following known issue. It seems to be a conflict issue between WPML and the latest version of the Site Kit by Google plugin. We got a few reports from other clients with the same error.
Our developers are investigating this issue. In the meantime, please consider downgrading to the previous Site Kit by Google(1.105) after a full site backup.